Cydia illutana is an univoltine species. Moths fly in May and June. The females deposit their eggs on young cones in the second half of June. The larvae feed in the cones and bore into the seeds. The excrements are ejected and remain, mixed with resin, attached to the cones. Excrements can also be deposited in the feeding tunnels. The larvae continue to feed in spring after hibernation. Pupation takes place inside a web on the soil, or in rotten wood, in May. Sacchiphantes or Chermes galls may also be attacked in years in which only a few cones are formed (Bogenschütz, 1991).

The feeding inhibits the maturing of the cones and the ejection of the seeds. Seed production is diminished by infestations of this species. Damage may be considerable in Finland and the northern part of Russia, where this species is frequently observed together with Cydia strobilella. Its economic importance, in comparison to that of Cydia strobilella, is in reality small, despite its frequent occurrence (Bogenschütz, 1991).

Distribution:

The species occurs from Western and Central Europe (UK, Netherlands, Austria, Germany, France) northwards into Scandinavia (Denmark, Norway, Sweden and Finland) and ranges eastwards into Russia (Siberia).